1. Field of the Invention
The present invention relates generally to the field of low-noise amplifiers. In particular, the present invention relates to the development of low-noise programmable gain amplifiers (PGAs) suitable for placement on integrated circuits (ICs) and for use in signal processing applications.
2. Related Art
PGAs are used in various analog signal processing applications where an electrical signal of varying amplitude must be either amplified or attenuated before subsequent signal processing. Various gain and/or attenuation settings are required to accommodate the wide dynamic range needed for the amplifier""s input stages. Numerous conventional techniques exist for meeting these demands.
What are needed, however, are techniques for providing attenuation in closed loop amplifiers without increasing their feedback factor. What is also needed is an approach to ensure suitable start-up conditions and avoid latchup, particularly in complimentary metal oxide semiconductor (CMOS) PGAs. Finally, a technique is needed to eliminate mismatched characteristics commonly found in passive elements across IC substrates due to process gradients.
The present invention includes a startup circuit including a comparing device configured to (i) receive a second circuit node voltage and a reference voltage as inputs, (ii) compare the received second circuit node voltage and the reference voltage, and (iii) produce a compensating voltage signal based upon the comparison. An active device has a control terminal connected to an output port of the comparing device and is configured to receive the compensating voltage signal. The active device also includes an output terminal connected to the control terminal of the second active device, and a common terminal connected to a first circuit node. Another active device has a control terminal connected to the output port of the comparing device and is configured to receive the compensating voltage signal. The other active device also has an output terminal connected to the control terminal of the first active device, and a common terminal connected to the first circuit node.